A conventional current-in-plane (CIP) read/write head in a disc drive typically includes a magnetoresistive (MR) read sensor deposited between insulating layers and outer magnetic shield layers. A conventional current-perpendicular-to-plane (CPP) read/write head in a disc drive typically includes a magnetoresistive (MR) read sensor deposited between magnetic shield layers. In the CPP read/write head the sensor is in direct contact with the shields, which are also used as the electrical contacts. The magnetoresistive read sensor typically includes a magnetoresistor stack, the electrical contacts and one or more biasing magnets that magnetically bias the magnetoresistor stack.
The magnetoresistor and the electrical contacts carry electrical sense current. As magnetically stored data on a disc passes by the magnetoresistor, the magnetoresistor generates readback pulses that have readback amplitudes that represent the data stored on the disc. The readback amplitude is generally proportional to the sense current. The sense current amplitude and read sensor dimensions are chosen in a way that considers the needs of the read channel electronics. The sense current amplitude and read sensor dimensions are also chosen in a way that considers the need to limit heating to prevent damage to the magnetoresistor. The need for a high amplitude readback pulse and the need to limit heating conflict with one another and limit the performance that can be achieved with conventional magnetoresistive read sensors.
In a conventional magnetoresistive read sensor, electrical sense current flows in a major plane that is parallel to the plane of the thin-films in the magnetoresistive sensor and parallel to the air-bearing surface of the magnetoresistor stack. These conventional read sensors are known as Current In-Plane (CIP) sensors. In response to the need for smaller and more sensitive read heads, some magnetoresistive read sensors have been developed where the electrical sense current flows perpendicular to the major plane of the magnetoresistor stack. These read sensors are known as Current Perpendicular-to-Plane (CPP) sensors. Depending on the dimensions, CPP sensors may have several advantages over the CIP sensors. CPP-SV (spin valves) and CPP-ML (multi layer) sensors have been shown to have some key advantages over CIP spin-valves. CPP devices have been shown to have a GMR effect at least as large as CIP devices, as current passes through every ferromagnetic/non-magnetic (FM/NM) interface without current shunting. In addition, for a CPP device, the sensor and shields are in direct contact with each other; thus, no insulating layer is needed between them. This decreases the shield-to-shield spacing and allows for the shields to also act as good thermal heat sinks. Having a good thermal heat sink allows for larger sense currents to be used, which translates to a larger readback pulse amplitude (Vpp).
However, the change from CIP sensors to CPP sensors has resulted in a new set of problems for head designers. For example, lead materials in CPP sensors generally have been limited to good magnetic shielding materials such as Ni80Fe20, which have relatively high electrical resistivity, therefore there is a need to reduce the electrical resistivity of the lead materials.
As the read sensor and lead materials are in contact with each other in a CPP sensor the lead materials act poorly as large thermally conductive heat sinks. Unfortunately, as the lead materials have been limited to good magnetic shielding materials, which have a relatively low thermal conductivity, there is a need for lead materials that have a higher thermal conductivity to prevent over heating.
High density magnetic recording readback sensors such as CIP and CPP spin valves, magnetic tunnel junctions and CPP multi-layers need to be biased/stabilized using a magnet. Most sensors have the high permeability shields in close proximity to the sensor and biasing magnet. This proximity results in a large amount of the flux from the magnet being lost to the shields instead of biasing/stabilizing the sensor. The use of magnetic shielding materials for the leads, such as Ni80Fe20, results in several negative features. For example, Ni80Fe20 has a fairly large anisotropic magnetic resistive (AMR) effect. This AMR effect can be seen as noise in a read back voltage. Ni80Fe20 also has a high electrical resistivity of approximately 20 μΩ-cm . The leads in a typical CPP head are in contact with the read sensor and act as large heat sinks. This is because Ni80Fe 20 has a relatively low thermal conductivity, that limits the maximum useable sense current for a spin valve. Therefore, it is desirable to reduce these effect to increase the efficiency of the sensor.
Perpendicular recording is a possible candidate for achieving high areal densities. One negative effect that has been identified in perpendicular recording is the Neighborhood Induced Transition Shift (NITS) effect. This effect comes from flux from adjacent tracks in the media entering the shields, traveling through the shields to the sensor and then down through the sensor into a soft underlayer on the disc and back to the original bit in the adjacent track. This creates a shift in the transfer curve that decreases the readback sensor dynamic range. Therefore there is a desire to limit the effects of NITS on the media in perpendicular recording.
Embodiments of the present invention provide solutions to these and other problems, and offer other advantages over the prior art.